Bruce Elliot Hirsch

Analysis of in vivo 3-D internal kinematics of the joints of the foot [MRI analysis]

This paper describes a methodology for the analysis of three-dimensional (3-D) kinematics of live joints of the foot based on tomographic image data acquired via magnetic resonance (MR) imaging. A mechanical jig facilitates acquisition of MR images corresponding to different positions of the joint in a pronation-supination motion. The surfaces of the individual tarsal bones are constructed by segmenting the MR images. A mathematical description of the motion of the individual bones and of their relative motion is derived by computing the rigid transformation required to match the centroids and the principal axes of the surfaces. The mathematically described motion is animated via surface renditions of the bones. The kinematics of the bones are analyzed based on features extracted from the motion description and on how they vary with motion. Based on 17 joints that have been imaged, which includes an abnormal joint and the same joint after surgical correction, the authors conclude that this methodology offers a practical tool for measuring internal 3-D kinematics of joints in vivo and for characterizing and quantifying with specificity normal kinematics and their pathological deviations. Some of the 3-D kinematic animations generated using the methods of this paper for normal joints can be seen at: http://www.mipg.upenn.edu.

Clinical Anatomy of the Quadriceps Femoris and Extensor Apparatus of the Knee

Most descriptions of the extensor mechanism of the knee do not take into account its complexity and variability. The quadriceps femoris insertion into the patella is said to be through a common tendon with a three-layered arrangement: rectus femoris (RF) most superficially, vastus medialis (VM) and lateralis (VL) in the intermediate layer, and vastus intermedius (VI) most deeply. We dissected 20 limbs from 17 cadavers to provide a more detailed description of the anterior components of the knee: the tendon, the patellar retinacula, and the patellofemoral ligaments. Only three of the 20 specimens exhibited the typically described quadriceps pattern. The remainder had bilaminar and even more complex trilaminar and tetralaminar fiber arrangements. We found an oblique head of the vastus lateralis (VLO), separated from the longitudinal head by a layer of fat or fascia, in 60% of the specimens. However, we found no distinct oblique head of the vastus medialis (VMO) in any specimen. The medial patellofemoral ligament (MPFL) was more common than the lateral (LPFL), supporting its suggested role as the principal passive medial stabilizer of the patella. Because the quadriceps muscle group plays a direct role in patellofemoral joint function, investigation into the clinical applications of its highly variable anatomy may be worthwhile with respect to joint dysfunction and failures of TKAs.

3D MR image analysis of the morphology of the rear foot: application to classification of bones

The purpose of this work is to characterize the three-dimensional (3D) morphology of the bones of the rear foot using MR image data. It has two sub-aims: (i) to study the variability of the various computed architectural measures caused by the subjectivity and variations in the various processing operations; (ii) to study the morphology of the bones included in the peritalar complex. Each image data set utilized in this study consists of sixty sagittal slices of the foot acquired on a 1.5 T commercial GE MR system. The description of the rear foot morphology is based mainly on the principal axes, which represent the inertia axes of the bones, and on the bone surfaces. We use the live-wire method [Falcao AX, Udupa JK, Samarasekera S, Shoba S, Hirsch BE, Lotufo RA. User-steered image segmentation paradigms: live wire and live lane. Proceedings of the Society of Photo-optical Instrumentation Engineers 1996;2710:278-288] for segmenting and forming the surfaces of the bones. In the first part of this work, we focus on the analysis of the dependence of the principal axes system on segmentation and on scan orientation. In the second part, we describe the normal morphology of the rear foot considering the four bones namely calcaneus, cuboid, navicular, and talus, and compare this to a population from the upper Pleistocene. We conclude that this non-invasive method offers a unique tool to characterize the bone morphology in live patients towards the goal of understanding the architecture and kinematics of normal and pathological joints in vivo.

New method of studying joint kinematics from three-dimensional reconstructions of MRI data.

A new method of measuring the kinematic parameters of joints has been developed. This article describes the procedure, using tarsal joints as examples. The method uses the technique of computerized three-dimensional reconstruction from magnetic resonance images, taken at regular intervals throughout a foots range of motion. From these reconstructions, various kinematic information, such as orientation of instantaneous axes, amounts of rotation, amounts and direction of translation, and bony contact areas, is derived. The method is noninvasive and can be applied to individual subjects or patients.

A characterization of the geometric architecture of the peritalar joint complex via MRI, an aid to classification of foot type

The purpose of this work is to study the architecture of the rearfoot using in vivo MR image data. Each data set used in this study is made of sixty sagittal slices of the foot acquired in a 1.5-T commercial GE MR system. The authors use the live-wire method to delineate boundaries and form the surfaces of the bones. In the first part of this work, they describe a new method to characterize the three-dimensional (3-D) relationships of four bones of the peritalar complex and apply this description technique to data sets from ten normal subjects and from seven pathological cases. In the second part, the authors propose a procedure to classify feet, based on the values of these new architectural parameters. They conclude that this noninvasive method offers a unique tool to characterize the 3-D architecture of the feet in live patients, based on a set of new architectural parameters. This can be integrated into a set of tools to improve diagnosis and treatment of foot malformations.

An in vivo analysis of the motion of the peri-talar joint complex based on MR imaging

The purpose of this work is to characterize the three-dimensional (3-D) motion of the peritalar joint complex in vivo using magnetic resonance imaging (MRI). Each image data set utilized in this study is made of 60 longitudinal MR slices of the foot in each of eight positions from extreme pronation to extreme supination. The authors acquired and analyzed ten such data sets from normal subjects, seven data sets from pathological joints and two postoperative data sets. They segmented and formed the surfaces of the calcaneus, talus, cuboid and navicular from all data sets. About 30 geometrical parameters are computed for each joint in each position. The results present features of normal motion and show how normal and abnormal motion can be distinguished. They also show the consequences of surgery on the motion. This non-invasive method offers a unique tool to characterize and quantify the 3-D motion of the rearfoot in vivo from MR images.

Rigid model-based 3D segmentation of the bones of joints in MR and CT images for motion analysis

There are several medical application areas that require the segmentation and separation of the component bones of joints in a sequence of images of the joint acquired under various loading conditions, our own target area being joint motion analysis. This is a challenging problem due to the proximity of bones at the joint, partial volume effects, and other imaging modality-specific factors that confound boundary contrast. In this article, a two-step model-based segmentation strategy is proposed that utilizes the unique context of the current application wherein the shape of each individual bone is preserved in all scans of a particular joint while the spatial arrangement of the bones alters significantly among bones and scans. In the first step, a rigid deterministic model of the bone is generated from a segmentation of the bone in the image corresponding to one position of the joint by using the live wire method. Subsequently, in other images of the same joint, this model is used to search for the same bone by minimizing an energy function that utilizes both boundary- and region-based information. An evaluation of the method by utilizing a total of 60 data sets on MR and CT images of the ankle complex and cervical spine indicates that the segmentations agree very closely with the live wire segmentations, yielding true positive and false positive volume fractions in the range 89%-97% and 0.2%-0.7%. The method requires 1-2 minutes of operator time and 6-7 min of computer time per data set, which makes it significantly more efficient than live wire-the method currently available for the task that can be used routinely.

Three-dimensional reconstruction of the foot from computed tomography scans.

Recently developed computer programs create a new type of image from the sections created in computed tomography. These images look like actual photographs of internal structures. The authors describe the process of three-dimensional reconstruction in nonmathematical terms, and provide examples of its use in imaging the bones of the foot. They demonstrate the techniques ability to resolve small details, and its usefulness in displaying articular surfaces.

Joint kinematics via three-dimensional MR imaging

The methodology reported here enables us to mathematically model and quantify the motion of each component bone, relative motion of bones, the contact surface of bones and their change during motion for complex joints, from a time sequence of MR image volumes. Additionally, since we model the bone surfaces, we are able to display in vivo joint motion. Through a variety of new rendering techniques we are able to create realistic displays of bones from MR images and to combine these displays with the motion parameters.

Kinematics of joints of the foot via three-dimensional; magnetic resonance images

A system which is being developed to carry out a kinematic analysis of joints and to provide data on joint motions is described. It is based on the registration of two three-dimensional reconstructions of the component bones of a joint from magnetic resonance scan data. The result of the registration is the movement necessary to transform one joint instance into another. The authors conclude that it is possible to create an accurate three-dimensional reconstruction of bones from magnetic resonance images, although it requires interactive segmentation of the bone by a knowledgeable operator.<<ETX>>